When I defeated brakayo without pistol specialisation I used the time's when he was out of reach to take care of the spawning guards (grenades and assult rifle). When he start chase you run and time how long time it takes for him to give up the chase (I counted to 20). After that there is a small window when he catches his breath where you can unload with prefered attack style before he escapes on the balcony again. After A couple of rounds like this the guards will stop spawning and he will never escape to the balcony again the periods between him chasining you will get smaller, but just use the same tacticts.
Against omen deng I didn't do anything special, just used all skills available and some first aid kit's.